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I live in a small (1-traffic-light) town in upstate NY. Some local village water officials accidentally cracked a water main (feeding water to the entire area) and so the Department of Health had to step in and issue a "Boil Water Alert" because the water could be contaminated.

The alert was in effect for almost a week (!!!!) and is now lifted. The village is recommending to everyone that they "flush out all water lines in [our houses]" to get rid of any potentially contaminated water.

Any ideas how I could do this properly? I have two young kids in the house and want to go by the book, for their sake. My wife thinks this is just as easy as running all the sinks and showers in the house for a few minutes. But...

  • Is it really just a few minutes? Or should we run everything for longer? We have a 98-gallon water heater.
  • Also, speaking of the water heater, doesn't that store hot water in some kind of separate compartment/tank than the cold water? If so, how do I flush out the hot water? Do I just run hot water?!?

I'm a software engineer, so by definition, I'm probably overthinking this. But I would feel just awful if one of my sons got really sick because of some laziness on my part.

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You could just run the water for as long as you think it would take. Probably would have to run the hot until the water runs cold, then a little longer. This would basically ensure the water heater is cleared and the piping before it. The cold wouldn't have to be ran as long, but your goal is to still clear the pipes out.

The best way to know that you've got all new water, and flush the house; is to shut off the main valve and then go to the lowest operable plumbing point in your house.

Like my water heater is in my basement and it's drain valve at the bottom is the lowest point in the house as the main water line comes in above this. So, because of gravity, most of the water in the house would drain out of this. If your heater isn't the lowest though, just search for the lowest drainage point.

Again just shut off the main valve so no new water will enter the system yet. If you go the route of through the heater, make sure to flip it's breaker. Go turn on all sink handles too, both hot and cold, so that air can be brought into the piping and released when the water comes back on.

Once it stops draining, your house is now 90+% empty. Close the valve back, (flip the heater's power back on), and turn back on the main water. You'll hear rumbling and such from the sinks that you opened as the air clears the lines. Once the water starts flowing from them like normal and there are no more sounds coming from the pipe, you're clear. You could run them for another minute or two (take a cold shower) for that last little bit of water that could have been left in the pipes.

This doesn't work any better than just running the water for an hour or however long as far as cleaning the system, but it could save you some water and you'll know when it's done.

Last, if the home or plumbing supplies are older, you might have flakes of rust and such from your pipes show up in the aerators or the sinks. Might not, but just remember this in the possibility that you're getting low pressure afterwards.

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    And if you get too many flakes of rust, maybe it is time to review the plumbing. You flush out the contaminated water and do a checkup of the plumbing at the same time.
    – Mindwin Remember Monica
    Commented Mar 4, 2016 at 14:55
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    regarding draining the pipes, this isn't always possible. The lowest drain point I'm aware of in my house is the bathtub faucet. all the other pipes (except of course for piping to actual fixtures) are embedded in the slab (single level residence).
    – Michael
    Commented Mar 4, 2016 at 15:33
  • While simply allowing the water to run for a lengthy amount of time will perform a reasonable flush, it won't be as complete as emptying all the lines possible, then flushing them all with fresh water for a period of time. Also, if the house has had any plumbing remodeling, and pipes have been capped rather than disconnected, then even a drain and flush may not be sufficient to fully clear the pipes. If you do only a flush, then don't use hot water for food or drinks for a week after, to give the water heater plenty of time to dilute and flush, only use cold water.
    – Adam Davis
    Commented Mar 4, 2016 at 15:44
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    Additionally, you could close the pipes, recharge the system and then drain again. Ultimately, there is going to some latent risk with any drinking water system, just like there is risk climbing out of bed. You ultimately have to decide how much risk to accept and not be paralyzed by it. Municipal waters systems are not sterile, shiny tubes.
    – RomaH
    Commented Mar 4, 2016 at 17:04
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If the water heater is up to normal temperature bacteria cannot survive there.

I think your wife is right ( I know that sucks 😞) but if you are still nervous about it then run your water longer and turn up the temperature on your water heater for a while. Make sure you run all your faucets including the outside hose bibs.

Good luck!

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    bacteria may not be the only concern.
    – Tester101
    Commented Mar 4, 2016 at 13:21
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    The bit about bacteria isn't true, either. Botulism spores can survive boiling water (you need a pressure cooker at 120 degrees C for 30 minutes to kill them).
    – ceejayoz
    Commented Mar 4, 2016 at 14:23
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I agree with ArchonOSX & it's probably you're best option based on level of experience. However, the Hose Bib would be the only & best option if it's attached before the Water Heater. If not, then I'd flush the system for an hour, see last paragraph.

If not, then maybe you have a neighbor that can assist or do the following for you. A much better alternative for the Water Heater is to drain the Water Heater & flush the line through it.

You'd shut off the gas & power to the Water Heater, close the hot & cold water valves above the Water Heater & open the top side valve to then open the bottom hose bib with hose attached to drain the Water Heater.

Once the Water Heater's drained, then you turn on just the cold water valve & let the water run through the empty tank & out of the hosed hose bib at the bottom...for at least 10-minutes.

Without the alternative above, a full Water Heater as big as yours could take an hour to reasonably fill with gunk & be diluted by clean water mixing in. There's also no reason to try & heat water while flushing, so turn the Water Heater off or way down & remove any faucet aerators.

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    Why "remove any faucet aerators"?
    – Yehuda_NYC
    Commented Mar 4, 2016 at 13:54
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    @Yehuda_NYC So any debris in the water doesn't get stuck in the aerator. Clearing the lines doesn't do you much good if you've got a nice buildup of dirt at the faucet.
    – ceejayoz
    Commented Mar 4, 2016 at 14:24
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We had a similar situation here in the UK last year where due to containments the water was unsafe to drink. The official advice here is simply:

Q: How do I know if my pipes are safe?

A: If you have been using your water as usual e.g. flushing the toilets, washing, showers and baths etc, then the water that we have been supplying to your home will have flushed any bugs out of your plumbing system.

If you have been away from home or your business has been closed, and no water has been flowing through the pipes, then you should run your tap for a short time to ensure that fresh mains water comes through.

If you don't drink the water from the hot storage tank, I see no need to have to empty it.

I can't say for certain that the US advice would be the same, but I don't see why it would be significantly different.

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